Temporomandibular joint disc position and configuration in children with functional unilateral posterior crossbite: A magnetic resonance imaging evaluation

ORIGINAL ARTICLE

Temporomandibular joint disc position and configuration in children with functional unilateral posterior crossbite: A magnetic resonance imaging evaluation Silmara Elena Papa Pellizoni,a Marco Antonio Canada Salioni,a Yara Juliano,b Antonio Sergio Guimarães,c and Luis Garcia Alonsod São Paulo, Brazil Introduction: Epidemiological studies have suggested an association between unilateral posterior crossbite (UPXB) and temporomandibular joint disc displacement. The purpose of this prospective study was to investigate articular disc positioning and its configuration in children with functional UPXB malocclusions and their counterparts with normal occlusions by using magnetic resonance imaging. Methods: The study sample included 9 girls and 6 boys (mean age, 9.3 years; SD, 2.1) with complete UPXB involving 3 or more posterior teeth and functional shift from centric relation to intercuspal position (patient group). The control group consisted of 10 girls and 6 boys (mean age, 9.6 years; SD, 2.1) with normal occlusion. All participants had no signs or symptoms of temporomandibular disorder. Sagittal and frontal magnetic resonance images of the temporomandibular joint with the jaw in closed and open positions were made bilaterally. Three investigators independently interpreted the magnetic resonance images. Results: No intergroup or intragroup differences regarding sex were found, and only 1 subject with articular derangement (disc displacement without reduction associated with disc distortion-folded disc) was found (patient group, same side of crossbite). Conclusions: These findings suggest that temporomandibular joint derangements and functional UPXB are independent occurrences, or that the magnitude of such derangements is still not normally detected by magnetic resonance imaging in children in this age range. Another explanation for posterior crossbite not being reflected in disc displacement is the potential compensatory asymmetrical condyle growth or articular fossa remodeling that can hold the articular disc in position. (Am J Orthod Dentofacial Orthop 2006;129:785-93)

T

he temporomandibular joint (TMJ) provides the articulation between the movable mandible and the fixed temporal bone of the cranium. It is a highly complex joint capable of a combination of hinge and sliding movements.1 In the temporal bone, the articular surface consists of an articular tubercle followed by a posterior fossa, which fits onto the articular surface on the top part of the mandible head. These articular surfaces are cushioned with an intermediary a

Doctorate student, Department of Morphology, Federal University of São Paulo, Escola Paulista de Medicina, São Paulo, Brazil. b Professor, Department of Preventive Medicine, Universidade de Santo Amaro, São Paulo, Brazil. c Researcher, Head Institute, Federal University of São Paulo, Escola Paulista de Medicina, São Paulo, Brazil. d Associate professor, Department of Morphology, Federal University of São Paulo, Escola Paulista de Medicina, São Paulo, Brazil. Reprint requests to: Silmara Elena Papa Pellizoni, Rua das Nogueiras, 70 Jardim Glória Americana, São Paulo, Brazil 13468-200; e-mail, pellizoni@ vivax.com.br. Submitted, August 2004; revised and accepted, November 2004. 0889-5406/$32.00 Copyright © 2006 by the American Association of Orthodontists. doi:10.1016/j.ajodo.2006.02.007

articular disc. The articular disc is round to oval and has a thick periphery and a thin central part. In the sagittal section, the disc appears biconcave and, in the frontal plane, crescent shaped. The anterior and posterior parts of the disc as seen in the sagittal plane are called the anterior and posterior bands.2 In the closed-mouth position, a normal disc has its posterior band centered at about the apex (12 o’clock position) of the condyle.3 As the jaw opens, the rounded apex of the condyle opposes the central thin part of the disc, under the articular tubercle.2,4 Different types of functional malocclusion (occlusal interferences) have been shown to be partly responsible for signs and symptoms of temporomandibular dysfunction (TMD) in children and adolescents,5-10 and functional unilateral posterior crossbite (FUPXB) might create a predisposition for mandibular dysfunction.7,11-16 Unilateral and bilateral posterior crossbite is characterized by the buccal cusps of the maxillary teeth in the canine, premolar, and molar regions occluding lingually to the buccal cusps of the corresponding 785

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Fig 1. Study model analysis. a, Lateral deviation of midline of lower occlusal table against upper one was measured as D Is-Ii; b, mesiodistal occlusal relationship of first molar was assessed with Angle classification.

mandibular teeth.17 It is the result of insufficient maxillary arch width compared with mandibular arch width.18 Such an arch-width reduction might be induced by environmental factors such as mode of breathing, swallowing pattern, or sucking habit (finger or dummy).19-22 Unilateral posterior crossbite (UPXB) is frequently observed in the deciduous and mixed dentition stages, with reported incidences of 7% to 23%.23-25 FUPXB, which accounts for 67% to 79% of all UPXB cases,11,23 includes the associated lateral displacement of the mandible toward the crossbite side in maximum intercuspation.6,11 Epidemiological studies have shown that crossbites are often associated with asymmetric condyle positioning, resulting in asymmetric facial features when the person’s mouth is closed.26-28 This abnormal positioning in a child could interfere with condylar growth and development, leading to TMJ problems. Weinberg29 and Mikhail and Rosen30 reported that asymmetric spaces between articular surfaces of the condyles and temporal bones tomographically determined are associated with disc derangement, TMJ pain, and muscle spasms. In contrast to previous studies, a longitudinal study by Egermark et al31 suggested that correlations between signs and symptoms of TMD and various malocclusions are generally nonexistent or weak. Magnetic resonance imaging (MRI) made possible the simultaneous imaging of both soft and hard tissues and is the imaging method of choice to study the

TMJ.32,33 The sensitivity, specificity, and accuracy of MRI of the TMJ for disc position and configuration were explored by Westesson et al34 in a study of 55 specimens from fresh cadavers. We investigated the positioning and configuration of the articular disc in children with normal and FUPXB malocclusions using MRI to determine whether crossbite has a deleterious effect on the articular disc. SUBJECTS AND METHODS

This study was carried out with 31 subjects aged 6 to 12.9 years in the mixed dentition. The patient group (n ⫽ 15) included 9 girls and 6 boys (mean age, 9.3 years; SD, 2.1) diagnosed with UPXB (8 left, 7 right) involving 3 or more teeth and functional mandibular shift from centric relation to intercuspal position (FUPXB). The control group (n ⫽ 16) comprised 10 girls and 6 boys (mean age, 9.6 years; SD, 2.1) with normal occlusions. All subjects received complete oral examinations in which intraoral, extraoral, and functional aspects were investigated. Intraoral examination and model analysis determined occlusal morphology and showed the crossbite and the median line discrepancy between the maxillary and mandibular incisors (Fig 1). The mean discrepancies between the maxillary and mandibular incisors were 2.42 mm in right FUPXB and 2.68 mm in left FUPXB. The mesiodistal occlusal relationship of the first molar was also assessed with the Angle classification. In right FUPXB, all children had

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Class II malocclusions; on the opposite side, 5 had Class I, and 2 had Class II. In left FUPXB, 6 children had Class II and Class I on the opposite side, and 2 children had Class I on the crossbite side and Class III on the opposite side. In left FUPXB, we found 5 children with mesofacial patterns and 4 with dolicofacial patterns. In right FUPXB, the facial patterns were 4 mesocephalic, 1 dolicocephalic, and 2 brachycephalic. In the normal occlusion group, 10 children had mesofacial patterns, 4 had brachyfacial patterns, and 2 had dolicocephalic patterns. Research diagnostic criteria were used to examine temporomandibular disorders.35 The TMJs were examined by signals (clicks, coarse crepitus, fine crepitus, and pain), digital palpation (digital pressure of 0.5 kg) in the lateral pole and posterior attachment, and functional manipulation. The extraoral muscles were palpated with digital pressure of 1.0 kg. The temporal muscles (anterior, middle, and posterior), masseter muscle (origin, body, and insertion), posterior mandibular region (stylohyoid and posterior digastric), and submandibular region (medial pterygoid, suprahyoid, and anterior digastric) were examined. Intraoral palpation (digital pressure of 0.5 kg) was done to evaluate the lateral pterygoid area and the tendon of temporalis. All muscles were palpated bilaterally. A questionnaire was completed to evaluate subjective mastication and general health conditions, tensional headaches, use of drugs (for pain in the orofacial region or headache, especially muscle relaxants and analgesics), parafunctional habits (clenching and bruxism), and the need for TMD treatment. The exclusion criteria were signs or symptoms of temporomandibular disorders. As part of the study records, frontal and lateral photographs of each participant with the mouth closed were taken. MRI

All subjects had their right and left TMJs imaged in frontal view with the mouth closed and in oblique sagittal view with the mouth in closed and wide-open positions in a 1.5-T imaging system (Sigma LX 9.1, General Electric, Medical Systems, Milwaukee, Wisc). Frontal imaging parallel to the horizontal long axis of the condyle was performed separately for the left and right TMJs, whereas the oblique sagittal imaging perpendicular to the horizontal long axis of the condyle was carried out simultaneously for both TMJs. The parameters for the sagittal proton-density images were as follows: repetition time (TR), 300 ms; echo time (TE), 12.1 ms; number of excitations (NEX), 2; and field of view (FOV), 14 cm. The frontal proton-density images were as follows: TR, 450 ms; TE, 9 ms; NEX, 2; and FOV, 18 cm. We used slice thicknesses of 4 mm (sagittal

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images) and 3 mm (frontal images) without skip and matrices of 320 ⫻ 224 pixels (sagittal images) and 256 ⫻ 224 pixels (frontal images). Scanning times were 47 seconds for the closed and open-mouth sagittal and frontal images. Initial localizers (TR, 300 ms; TE, 8 ms; NEX, 1; FOV, 24 cm; matrix of 256 ⫻ 128 pixels) were used for planning the sagittal images. At the least 1 investigator was present at all MRI procedures to ensure image quality and that the subjects were instructed to keep the teeth in proper contact during the closed-mouth examinations. Imaging assessment of the articular disc

Both articular discs of each subject were assessed for posteroanterior positioning, lateromedial displacement, and configuration. Magnetic resonance images were independently assessed by 3 investigators. When there was agreement between 2 investigators, that diagnosis was used. When there was no agreement, a consensus diagnosis was reached. The classification of anteroposterior disc positioning relative to the condyle was done according to the criteria of Murakami et al,36 which used closed and open-mouth sagittal images. On the closed-mouth image, a line (HO) was drawn joining the lowest point on the articular tubercle (e), and the lowest point on the postglenoid process (g). A second line (H1) was drawn parallel to HO passing through the most anterior point of the functional surface of the condyle (a). Two additional parallel lines were then drawn—line L1 perpendicular to H1 at the posterior edge of the functional condylar surface and line L2 perpendicular to H1 at point a. Lines H1, L1, and L2 were determined for compartments A, B, C, and D as shown in Figures 2 and 3, a and d. On the open-mouth image, a line (P) was drawn joining the closest points between the articular tubercle (Fig 3, b) and the condyle (Fig 3, c). Line P determined the anterior (WO) and posterior (SR) regions (Figs 2 and 3, b and e). The determination of sideways displacement of the articular disc was made according to the criteria of Katzberg et al.37 On the frontal image, the position of the disc was classified as normal if it was centrally positioned over the condylar head, and medially or laterally dislocated according to the positioning shown on MR imaging (Fig 3, c and f ). Discs having their posterior bands in compartment A (12 o’clock position) in the closed-mouth position and in region SR fin the open-mouth position were considered normally located. To assess configuration, the disc was categorized according to its shape as shown in Figure 4. Biconcave

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Fig 2. Criteria for disc position. Disc position was classified according to whether posterior band was in compartment A, B, C, or D in closed-mouth position, and in SR or WO in open-mouth position. A, 12 o’clock position was considered normal; B, still normal; C, partially displaced to anterior position; D, completely displaced. HO, tangent from postglenoid process (g) to articular tubercle (e). H1, line parallel to HO passing anterior edge (a) of functional surface of condyle. L1, line perpendicular to HO passing through superior edge (p) of functional surface. L2, line perpendicular to HO passing through anterior edge (a) of condylar function surface. P, line passing through point at which condyle is closest to articular tubercle.

Fig 3. Typical sagittal magnetic resonance images. a, Posterior band of disc (arrow) is in compartment A; b, in compartment SR in open-mouth position. Disc configuration is biconcave. Frontal image. Disc (arrow) is located superior to condyle (c), normal disc position (a, b, and c are same subject). d, Posterior band (arrow) of disc is in compartment D; e, in compartment WO in open-mouth position. Disc configuration is biplanar and becomes folded on opening. Frontal image. Disc (arrow) appears slightly thickened and is located slightly medial to condyle (f ) (d, e, and f are same subject).

configuration was considered normal, and the others were classified as altered. The Fisher exact test and the chi-square test were used to compare the altered positions of the discs and the configuration prevalence rates between the patient and control groups.

RESULTS

A total of 62 joints were examined, and the results are summarized in Tables I through IV (disc positioning and configuration, sagittal imaging) and Table V (disc sideways displacement, frontal imaging).

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Fig 4. Classification of disc configurations. Biconcave, both upper and lower surfaces are concave; biplanar, disc is of even thickness; hemiconvex, upper surface is concave, and lower is convex; biconvex, both upper and lower surfaces are convex; folded, disc is folded at center. Table I. Patient group disc positioning and configuration (sagittal imaging) Closed mouth

Biconcave Biplanar Hemiconvex Total

Open mouth

A

C

D

Total

SR

WO

24 4 0 28

0 0 1 1

0 1 0 1

24 5 1 30

24 4 1 29

0 1* 0 1

*Folded.

Table IV.

Alteration Group FUPXB patients Controls Total

Biconcave Biplanar Hemiconvex Total

Table III.

Open mouth

A

C

Total

SR

WO

26 5 0 31

0 0 1 1

26 5 1 32

26 5 1 32

0 0 0 0

Disc positioning Alteration

Group FUPXB patients Controls Total

Present

Absent

Total

% present

1 1 2

14 15 29

15 16 31

6.7 6.3 6.5

P ⫽ .7419.

The distribution of crossbite types in the patient group was even: 8 patients had left FUPXB, and 7 had right FUPXB. No disc features in the study patients, whether normal or abnormal, or on the left or right, had

Absent

Total

% present

6 6 12

10 9 19

16 15 31

37.5 40.0 38.7

Disc sideways positioning (frontal imaging)

Table II.

Closed mouth

Present

P ⬇ .9; ␹2 ⫽ 0.02; ␹2crit. ⫽ 3.84. Table V.

Control group disc positioning and configuration (sagittal imaging)

Disc configuration

FUPXB patients Controls Total

Central

Medial

Total

29 32 61

1 0 1

30 32 62

a statistically significant relationship with the type of crossbite. A total of 30 TMJs were studed in the patient group. With the mouth closed, 28 discs (93.3%) had their posterior bands in compartment A (normal positioning), 1 disc (3.3%) was in compartment C (partially displaced to an anterior position), and 1 disc (3.3%) was in compartment D (totally displaced, same side as crossbite). With the mouth open, all discs previously (with mouth closed) found having their posterior bands in compartments A and C (96.7%) had their posterior bands in region SR (normal positioning). Only 1 disc (3.3%) that was in total anterior displacement had its posterior band in region WO (abnormal positioning) when the subject had his mouth open, indicating no reduction of the disc to normal position (Table I). Regarding configuration, 24 discs (80.0%) were biconcave (normal configuration), 4 discs (13.3%) were biplanar, and 1 disc (3.3%) was hemiconvex, with both

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Table VI.

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Sex differences Disc positioning alteration

Group Male FUPXB patients Female FUPXB patients Male controls Female controls Total

Disc configuration alteration

Present

Absent

% present

Total

Present

Absent

% present

0 1 0 1 2

6 8 6 9 29

0.0 11.1 0.0 10.0 6.5

6 9 6 10 31

1 5 3 3 12

5 4 3 7 19

16.7 55.8 50.0 30.0 38.7

latter configurations considered to be altered. One biplanar disc was folded at its center when the subject’s mouth was open (Table I). In the control group, 32 TMJs were examined; 31 discs (96.9%) were functionally normal—posterior disc band in compartment A with closed mouth and in SR region with open mouth. Only 26 discs (81.3%) had normal function and configuration (biconcave). Partial anterior displacement of the articular disc (n ⫽ 1; 3.1%), and biplanar (n ⫽ 5; 15.6%) and hemiconvex (n ⫽ 1; 3.1%) configurations were also present in the control group (Table II). The investigation of sideways displacement of the articular disc (frontal imaging) showed that only 1 disc (3.3%) was not centered over the condyle (medially displaced) in the patient group. There were no cases in the control group of sideways altered positioning (Table V). Sex differences regarding disc positioning and configuration were not statistically significant (Table VI). The statistical test comparing abnormal occurrences between the patient and control groups as to disc positioning and configuration showed no statistically significant difference (disc positioning, Fisher exact test, P ⫽ .7419; disc configuration, Fisher exact test, P ⬇ .9; chi-square test ␹2 ⫽ 0.02 and ␹2critical ⫽ 3.84; Tables III and IV, respectively). DISCUSSION

Irrespective of the type of occlusion, internal TMJ derangements— disc displacement with or without reduction and osteoarthrosis—involve symptoms such as pain, noise, and limitation of mouth opening in adults.38,39 Pullinger et al,40 studying 11 types of malocclusion in adults, found that patients with UPXB were more likely to have disc displacement with or without reduction, osteoarthrosis with disc displacement history, and primary osteoarthrosis. MRI studies established that, in the closed-mouth position, the articular disc should be considered to have normal positioning when its posterior band is situated at about apex of the mandibular condyle (12 o’clock

position or ⫾ 5° away),3,33,41 whereas normal configuration and positioning in closed-mouth position occurred when the disc assumed a bow-tie shape, with its thin intermediate region interposed between the mandibular condyle and the articular eminence.3 A more detailed scheme to study the positioning of the articular disc was proposed by Murakami et al.36 On sagittal imaging of the TMJ with the subject’s mouth closed, the articular space was divided into 4 compartments—A, B, C, and D. Discs with their posterior bands in compartments A and B were considered normally placed. Murakami et al36 added an objective scheme to classify normally positioned discs for assessing subjects with their mouths open. On a second sagittal imaging with the subject’s mouth open, the authors divided the articular space into regions SR and WO; normal discs have their posterior bands in SR. Therefore, we adopted that scheme to classify disc positioning. In our study, the imaging of subjects with mouths closed showed 2 discs (6.7%) in the patient group, in the same subject, abnormally positioned—1 (3.3%) in compartment C (partially displaced to an anterior position) and 1 (3.3%) in compartment D (totally displaced). In the control group, 1 disc (3.1%) was also found partially displaced (compartment C). Both discs in compartment C were seen with their posterior bands in region SR in sagittal imaging with open mouth, indicating disc reduction. Such a reduction was not observed for the disc in compartment D. This fact agrees with the finding of Murakami et al36 that the more anteriorly positioned the disc is in closed-mouth imaging, the less probable the disc reduction when the subject opens his mouth. Although our sample was small for statistical analysis, the 3 discs found to be irregularly positioned were in female subjects (Table VI), a result that might be related to the higher prevalence of disc displacement found in female patients by Solberg et al,42 Kirkos et al,43 and Nebbe and Major.44 Nebbe and Major44 also found that medial sideways disc displacement was more prevalent than lateral displacement, which also occurred in our study (Table V).

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Regarding the configuration of discs with displaced positioning—the 3 discs referred above—2 discs in compartment C were hemiconvex, and the disc in compartment D was biplanar when the subjects had their mouths closed. These configurations changed into biconcave and folded, respectively, when the subjects opened their mouth. This behavior agrees with the observation of Murakami et al36 that discs in compartments A, B, and C when subjects had their mouths closed showed mostly biconcave configuration (⬎88%) in the open-mouth imaging, whereas most of those in compartment D in closed-mouth imaging became distorted in open-mouth position. The association between greater anterior disc displacement and greater disc distortion suggests that the posterior band of discs in compartment D are subject to increased compression exerted by the condyle during chewing movements, a potential factor of disc disconfiguration. It seems logical to consider crossbite as a potential factor in the development of TMD. Our study is far from providing evidence either for or against such reasoning because of our small number of subjects; however, only 2 were found to have disc displacement, 1 in the crossbite group and 1 in the control group, suggesting that disc displacement also involves other factors, because the control group included subjects without malocclusion. Kirkos et al,43 investigating disc positioning with MRI in 21 asymptomatic and clinically normal volunteers aged 23 to 43 with no history of TMJ disorders, found that 62% had articular discs anteriorly displaced; these authors suggested that anterior disc displacement could be either a predisposing factor to TMJ dysfunction or simply an anatomic variation. Westesson et al45 reported that 15% of the 40 healthy subjects with asymptomatic and clinically normal TMJs had displaced articular discs and concluded that disc displacement does not necessarily cause functional abnormalities such as clicking, irregular movements, or opening limitations. Our findings add to those studies, showing no definite association between crossbite and TMJ disorders such as disc displacement. We found no significant difference between the posterior crossbite group and the control group for disc displacement (P ⫽ .7419; Fisher exact test) or disc configuration (P ⬇ .9; Fisher exact test; ␹2 ⫽ 0.02 and ␹2critical ⫽ 3.84). Functional appliance therapy can induce alterations in morphology and in the mandibular position such as extensive bone formation along the glenoid fossa and condyle and increased proliferation of condylar cartilage.46 A similar, but less intense, mechanism can occur in children with FUPXB because, with the median line mandibular deviation associated with new mandibular

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posture, the opposite side can simulate a functional appliance. This can help us to understand asymmetry of children’s condyles,26,28 which progressively tend to be symmetric in adulthood.16,47 There was no relationship between lateral pterygoid muscle and TMJ internal derangements.48 In parafunctional activities and heavy mastication, the lateral pterygoid muscle is believed to play a role in TMD.49 On the other hand, a positive association was observed between this muscle and disc displacement, although it is not considered the main factor in the displacement genesis.50,51 Probably these disarrangements are the sum of various components (bone structure, muscles, disc position), and, in each person, at least 1 of them could play a different role.52 In children with UPXB, with the mandible at rest, anterior temporal muscle activity was strongest on the side of normal occlusion, and, in the posterior temporal muscle, it tended to be strongest on the crossbite side. During maximum bite, the action of the posterior temporal muscle was reduced on the side with normal occlusion compared with the crossbite side.53,54 The activity of the masseter muscle was not modified.55 Studies investigating the association between posterior crossbite and TMJ problems other than disc displacement show varying results. Lieberman et al56 found no significant relationship between posterior crossbite and TMD symptoms; Celic et al57 found that TMD signs were weakly associated with posterior crossbite; Vanderas58 reported a significant correlation between pain in the temple region and posterior crossbite in children with calm traits but not in their noncalm counterparts; Sari et al59 found that the association between posterior crossbite and TMD was not significant in children in the permanent dentition, but it was significant in children with mixed dentition; Egermark et al,31 in a 20-year follow-up study, concluded that the association between different malocclusions and TMD are nonexistent or weak; Tanne et al,60 Motegi et al,61 and Miyazaki et al14 studied only patients with TMD and malocclusions, reporting increased prevalence of pain in the TMJ or related region, difficulty in jaw movement, and clicking in patients with posterior crossbite. Studying specifically the relationship between posterior crossbite and TMJ noise, Keeling et al62 reported it to be nonsignificant, Thilander et al63 reported it to be significant, and Riolo et al10 found a significantly higher prevalence of joint sounds in older children with crossbites. These discrepant findings about the association between malocclusion and TMD symptoms and signals are probably related to differences in methodology such as type and size of the

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samples, and the details used in malocclusion diagnosis, and the criteria to classify signs and symptoms of TMD. CONCLUSIONS

These findings suggest that TMJ derangements and FUPXB are independent occurrences, or that the magnitude of such derangements is still not normally detected by MRI in patients in this age range. Another explanation for posterior crossbite not being reflected in disc displacement is the potential compensatory asymmetrical condylar growth or articular fossa remodeling that can hold the articular disc in position. Even though such compensatory changes are less likely in children, further studies should investigate this phenomenon in normal children with FUPXB.

REFERENCES 1. Pertes RA, Gross SG. Functional anatomy and biomechanics of the temporomandibular joint. In: Pertes RA, Gross SG, editors. Clinical management of temporomandibular disorders and orofacial pain. Chicago: Quintessence; 1995. p. 1-12. 2. Katzberg RW, Westesson PL. Temporomandibular joint imaging. In: Som PM, Bergeron RT, editors. Head and neck imaging. St Louis: Mosby; 1991. p. 349-78. 3. Rao VM, Bacelar MT. MR imaging of temporomandibular joint. Magn Reson Imaging Clin N Am 2002;10:615-30. 4. Chaudhary A, Appelbaum J, Schneck M, Lorenzo N. Temporomandibular joint syndrome. eMed J 2002;3:1-10. 5. Egermark-Eriksson I, Ingervall B. Anomalies of occlusion predisposing to occlusal interference in children. Angle Orthod 1982;52: 293-9. 6. Egermark-Eriksson I. Malocclusion and some functional recordings of the masticatory system in Swedish schoolchildren. Swed Dent J 1982;6:9-20. 7. Egermark-Eriksson I, Ingervall B, Carlsson GE. The dependence of mandibular dysfunction in children on functional and morphologic malocclusion. Am J Orthod 1983;83:187-94. 8. Nilner M. Epidemiology of functional disturbances and diseases in the stomatognathic system. Swed Dent J 1983;17[suppl]:1-44. 9. Egermark-Eriksson I, Ingervall B, Carlsson GE. A long-term epidemiologic study of the relationship between occlusal factors and mandibular dysfunction in children and adolescents. J Dent Res 1987;66:67-71. 10. Riolo ML, Brandt D, TenHave TR. Associations between occlusal characteristics and signs and symptoms of TMJ dysfunction in children and young adults. Am J Orthod Dentofacial Orthop 1987;92:467-77. 11. Thilander B, Wahlund S, Lennartsson B. The effect of early interceptive treatment in children with posterior crossbite. Eur J Orthod 1984;6:25-34. 12. Mohlin B, Thilander B. The importance of the relationship between malocclusion and mandibular dysfunction and some clinical applications in adults. Eur J Orthod 1984;6:192-204. 13. Egermark-Eriksson I, Carlsson GE, Magnusson T, Thilander B. A longitudinal study on malocclusion in relation to signs and symptoms of craniomandibular disorders in children and adolescents. Eur J Orthod 1990;12:399-407.

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